Circulating breast epithelial antigens (CBEAgs) released into the blood stream detect tumors and inform on the Ag make-up of the tumor. We developed sensitive and specific techniques for CBEAgs identification and extraction from serum. Our monoclonal antibodies (MoAbs) identify several CBEAgs and determine their serum levels, study their metabolism and their participation in immunocomplexes. Thus, we continue to create MoAbs against CBEAgs and use them in diagnostic and in host immunoresponse studies and at the morphological level to determine how they are released. With these approaches, we plan to: a) continue isolating and characterizing these CBEAgs. Using different isolation procedures, conditioned by the source of the Ags (free or in immunocomplex form) their Ag heterogeneity and degradation will be examined; b) study the fate of CBEAgs in the circulation (their physicochemical state, catabolic destruction, etc.); c) investigate how these CBEAgs are released and enter the circulation at the EM level; d) investigate the clinical significance of these CBEAgs, their associated antibodies and circulating immunocomplexes (CIC), and their ability to monitor benign and malignant lesions of the breast. Concurrently, we will investigate how isolated CBEAgs and their corresponding MoAbs may affect immunoreactants of breast cancer patients of varying tumor burden; e) determine the impact of these CBEAgs on the hosts' cellular immune response. Our ability to identify CBEAgs enables us to characterize a tumor mass by its Ag make-up from just a serum sample, determination that could be of therapeutic and/or prognostic value. In addition, knowledge of integrity and physicochemical status of these CBEAgs in circulation and how they are disposed of could help assess the patient's immune status. The ultrastructural study of the release of these CBEAgs could provide us with understanding about the way in which the tumor interacts with the host at the cellular level, while experimentation that we also propose will focus on the influence of these CBEAgs on the cellular immunity of the breast cancer patient.